The changes are expected to go into affect no later than October 1, 2013.

The move had been expected for weeks and is widely seen as part of Panetta's effort to finish as much as he can in extending benefits to gays and lesbians before leaving the Pentagon.

Facing legal limitations around the Defense of Marriage Act, some benefits will not be extended. This includes health care coverage, Pentagon officials said.

"One of the legal limitations to providing all benefits at this time is the Defense of Marriage Act, which is still the law of the land. There are certain benefits that can only be provided to spouses as defined by that law, which is now being reviewed by the United States Supreme Court," Panetta said in a statement.

The Defense of Marriage Act defines marriage as that between a man and a woman. Federal courts have ruled it unconstitutional and the Supreme Court has agreed to hear an appeal.

Pentagon officials briefing reporters on the change also said the agency did not extend housing benefits to same sex-couples.

This was due in part to feedback from troops who felt they might have problems getting military housing, which is in short supply at times. But there may also be legal issues to be resolved before such housing can be granted.